Added the ability to switch weapons

-Right-click for now to switch between the Sword and Warhammer
-Made Die() in LevelObject.cs virtual and take in a Level as a paramter

-Moved the PrevAttack timer to Weapon.cs and a corresponding Attack() method that plays the sound and updates the attack timer
-Added an Available field that denotes if the weapon is available or not for use (determines if it can be switched to)

-Added a Gold field in Enemy.cs that denotes how much gold an enemy receives when killed
-Made enemies give gold when killed by overriding the Die() method to give the player gold based on the enemy's Gold field
Designed More of the Game HUD

-Added a button for the Pause Menu
-Added the Gold icon and text
-Added XAML Styles for all controls
-Added a small fix to Game1.cs to prevent multiple CoreWindow.KeyDown events from being active at once
Merge remote-tracking branch 'origin/SwitchingWeapons' into HUDImprovements
Coded Functionality Into the HUD

-Made the Gold Amount update when the player's Gold changes
-Made the Weapon buttons switch to the corresponding weapon when clicked or tapped
Made enemies attack the Player Castle upon approaching it, making the castle lose health

-Added a new enemy Action called MeleeAttack
-Added Debug.cs, which aids in debugging by enabling us to toggle drawing Hitboxes and Hurtboxes on or off
  -Hold Left Shift, then press the Left arrow key for toggling Hurtboxes or the Right arrow key for toggling Hitboxes
  -More will be added to it later as we see fit
Started Designing the Shop's Interface

-Updated the player's gold on the UI when the game is started
-Updated the player's health whenever he loses/gains health
-Made the Pause button work on GamePage.xaml
-Started setting up the shop interface
Refined ShopItems by adding new fields like Cur and MaxLevels (# of times they can be upgraded), added some more of them, and added a Fade class which we can use for sprites and such
Merge branch 'EnemyAttacking' into StartShopDesign
Merge branch 'StartShopDesign'